var obj = {
  a: "a",
  b: undefined,
};
console.log("a" in obj);
console.log("b" in obj);
console.log(obj.hasOwnProperty("a"));
console.log(obj.hasOwnProperty("b"));

// function Person() {
//   this.name = "person";
// }
// Person.prototype.age = 22;
// var fun = new Person();
// console.log(fun.name);
// console.log(fun.age);
// console.log(fun.hasOwnProperty("name"));
// console.log(fun.hasOwnProperty("age"));
